The present invention relates generally to the field of miniature solid-state electronic devices. More specifically, it relates to that class of such devices in which a component is carried on a substrate and enclosed within a housing, and in which the housing is sealingly attached to the substrate. The present invention provides an improvement in the attachment of the housing to the substrate.
In many miniature electronic devices, such as, for example, miniature trimming potentiometers, an electronic component is mounted or formed (e.g., by thick film printing) on the surface of a ceramic substrate, along with its associated conductive leads and termination pads. Terminal leads, for mounting the device directly on a printed circuit board or installing the device in a socket, are attached (as by soldering) to the termination pads, and the surface of the substrate carrying the component is enclosed within a housing.
It is frequently necessary that the housing be attached to the substrate in such a way as to form an hermetic seal therebetween. Typically, this has been accomplished by using an adhesive cement which sealingly bonds the housing to the substrate. A significant disadvantage to this attachment method is that the housing and substrate must be mechanically held together while the cement cures. Another disadvantage is that different temperature coefficients of expansion among the cement, the plastic of the housing, and the ceramic of the substrate can result in a loss of seal integrity when the electronic device is exposed to high temperatures.
The prior art has addressed these problems by employing various types of mechanical clips to keep the housing sealingly attached to the substrate. Such clipping mechanism have proven cumbersome to use and they have added complexity and cost to the manufacturing process.
There has thus been a long-felt, but as yet unfulfilled need for a way to provide an hermetic seal between the housing and the substrate which avoids the use either of cement, or of complex and cumbersome clip-type mechanisms.